No description available.

One of the most challenging questions surrounding the Clovis colonization of North America is the character and structure of terminal Pleistocene environments, including floral and faunal communities. A series of cores in the mouth of an arroyo revealed late Pleistocene - early Holocene wetland sediments buried 12 meters below surface, at the approximate elevation of the entrenched modern San Pedro River channel. A suite of ¹⁴C dates show that wetlands of the ancestral San Pedro River occupied portions of the inner valley coincident with the Younger Dryas (13,000 - 11,500 cal yr BP) and the early Holocene (10,000 - 9,500 cal yr BP). A lack of Sporormiella fungal spores indicates that mammoths were rare or absent when Clovis populations appeared in the valley around 12,800 cal yr BP. Palynological and stable carbon isotope analyses show that C₄ grasses increased at 9,940 cal yr BP, just prior to frequent burning after 9,510 cal yr BP and rapid erosion at 9,470 cal yr BP. δ ¹⁸O values from soil carbonates vary but do not record a systematic shift in precipitation source or temperature during the late Pleistocene - early Holocene transition. The establishment of C₄ grasslands in the inner valley correlates with widespread changes in the Chihuahuan Desert flora around 10,000 cal yr BP. A relatively dense accumulation of Clovis-mammoth associations in San Pedro Basin contrasts the lack of megaherbivores indicated at Palominas Arroyo. The upper San Pedro Basin of southeastern Arizona contains a minimum of four Clovis-mammoth associations, making it possibly one of the densest concentrations of human-proboscidean sites on earth in terms of time and space. I use the Younger Dryas-age stratum known as the "black mat" to compare the Clovis-age archaeofaunal record of the basin to its paleontological background in order to measure the level of human predation that created this remarkable record. This analysis indicates that Clovis people were affecting the last mammoth populations to a significant degree, a situation expected only in the presence of abundant mammoths. I argue that this condition was met in the San Pedro Basin, possibly in the form of a terminal Pleistocene refugium. If the refuge hypothesis indeed explains mammoth predation, then Clovis-mammoth associations should occur as clusters as they do in the San Pedro Basin rather than as isolates as they are known to occur elsewhere. The use of radiocarbon frequency distributions to reconstruct prehistoric human and animal populations must account for taphonomic loss and other factors that affect the archaeological and paleontological records. Surovell et al. (Journal of Archaeological Sciences, 36, 1715–1724) have recently proposed a volcanic-based correction factor for removing "taphonomic bias" from temporal frequency distributions. Analysis of 718 radiocarbon dates sampled from the alluvium of the San Pedro and Santa Cruz Rivers and their tributaries in southeastern Arizona shows that discovery and scientific biases play an equally important role in the creation of radiocarbon frequency distributions, and that "taphonomic bias" has not been systematic through time. The latter principle is further demonstrated using a sample of 123 Pliocene to Clovis-age proboscideans from the San Pedro Valley. We propose an alternative model that is based on the nature of the stratigraphic record, with discovery bias, scientific bias, taphonomic loss, and the shape of the calibration curve all operating to influence the temporal frequency distribution of prehistoric phenomena.

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No description available.

Cette thèse a pour objet d'améliorer la connaissance du mécanisme de formation de suie. Deux méthodes ont été utilisées pour produire des particules de suie dans des conditions contrôlées : le brûleur à flamme plat où les particules se forment par combustion de mélanges d'éthylène/air riches et le tube à choc dans lequel la suie est produite par pyrolyse de C2H4 à haute pression (5 bar) et dans un large domaine de température (1850-2100 K). Ces deux systèmes ont été équipés avec un dispositif original de diffusion laser à trois angles couplé à l'extinction laser pour suivre la croissance de particules, identifier les différentes étapes de leur mécanisme de formation et en déduire l'évolution de la fraction volumique des suies, leur rendement, leur structure et leur morphologie. Dans la flamme, l'addition de H2 entraîne une réduction globale de la concentration des suies, de leur diamètre moyen des particules et leurs agglomérats, de la densité en nombre de particules. Dans le tube à choc, on n'observe pas de dépendance significative du délai d'induction à la formation des particules par addition de H2. La courbe de rendement en suie en fonction de la température présente la même forme avec et sans hydrogène mais le rendement maximal est fortement abaissé en présence d'hydrogène pour une concentration initiale fixée en atomes de carbone. Le rôle de l'hydrogène sur la croissance des particules et les caractéristiques des suies est discuté en comparant les résultats obtenus dans le cas de la flamme de prémélange et derrière l'onde de choc réfléchie respectivement.

The experiments reported in the present thesis examined the behavioural processes of Pavlovian fear extinction and latent inhibition. The first series of experiments studied the reacquisition of extinguished fear responses following different amounts of extinction training. Rapid reacquisition occurred when rats were reconditioned after moderate extinction, showing that the original learning remained intact across this extinction. In contrast, when reconditioning was given after massive extinction, reconditioned responding was first depressed but then spontaneously recovered over time. This suggests that massive extinction produces a relatively permanent loss of the originally learned responding, while additionally imposes on the extinguished CS a transient latent inhibitory process that prevented the immediate but not the delayed expression of reconditioning. The second series of experiments studied the impact of spontaneous recovery of extinguished fear responses on their additional extinction. These experiments demonstrated that a CS that had time to show spontaneous recovery underwent greater response loss across additional extinction than one lacking recovery. They also showed that an excitor extinguished in compound with a CS showing recovery suffered greater response loss than an excitor extinguished in compound with a CS lacking recovery. Further, extinction of a compound composed of two CSs, one showing recovery and a second lacking recovery, produced greater extinction to the CS that showed recovery. These results show that spontaneous recovery of extinguished responses deepens their extinction through an error-correction mechanism regulated by both common and individual error terms. The third series of experiments studied the spontaneous recovery of latently inhibited and extinguished fear responses in within-subject designs. Using a compound test procedure, a CS that had received extensive preexposure or extensive extinction was found to have undergone greater spontaneous recovery relative to a CS just moderately preexposed or moderately extinguished. A CS given a mixed history of preexposure and extinction also underwent greater recovery relative to a CS just preexposed or just extinguished. These results suggest that both latent inhibition and extinction share a transient depressive process, and that the resulting recovery of responding is proportional to the amount of this depression.

The experiments reported in the present thesis examined the behavioural processes of Pavlovian fear extinction and latent inhibition. The first series of experiments studied the reacquisition of extinguished fear responses following different amounts of extinction training. Rapid reacquisition occurred when rats were reconditioned after moderate extinction, showing that the original learning remained intact across this extinction. In contrast, when reconditioning was given after massive extinction, reconditioned responding was first depressed but then spontaneously recovered over time. This suggests that massive extinction produces a relatively permanent loss of the originally learned responding, while additionally imposes on the extinguished CS a transient latent inhibitory process that prevented the immediate but not the delayed expression of reconditioning. The second series of experiments studied the impact of spontaneous recovery of extinguished fear responses on their additional extinction. These experiments demonstrated that a CS that had time to show spontaneous recovery underwent greater response loss across additional extinction than one lacking recovery. They also showed that an excitor extinguished in compound with a CS showing recovery suffered greater response loss than an excitor extinguished in compound with a CS lacking recovery. Further, extinction of a compound composed of two CSs, one showing recovery and a second lacking recovery, produced greater extinction to the CS that showed recovery. These results show that spontaneous recovery of extinguished responses deepens their extinction through an error-correction mechanism regulated by both common and individual error terms. The third series of experiments studied the spontaneous recovery of latently inhibited and extinguished fear responses in within-subject designs. Using a compound test procedure, a CS that had received extensive preexposure or extensive extinction was found to have undergone greater spontaneous recovery relative to a CS just moderately preexposed or moderately extinguished. A CS given a mixed history of preexposure and extinction also underwent greater recovery relative to a CS just preexposed or just extinguished. These results suggest that both latent inhibition and extinction share a transient depressive process, and that the resulting recovery of responding is proportional to the amount of this depression.

The experiments reported in the present thesis examined the behavioural processes of Pavlovian fear extinction and latent inhibition. The first series of experiments studied the reacquisition of extinguished fear responses following different amounts of extinction training. Rapid reacquisition occurred when rats were reconditioned after moderate extinction, showing that the original learning remained intact across this extinction. In contrast, when reconditioning was given after massive extinction, reconditioned responding was first depressed but then spontaneously recovered over time. This suggests that massive extinction produces a relatively permanent loss of the originally learned responding, while additionally imposes on the extinguished CS a transient latent inhibitory process that prevented the immediate but not the delayed expression of reconditioning. The second series of experiments studied the impact of spontaneous recovery of extinguished fear responses on their additional extinction. These experiments demonstrated that a CS that had time to show spontaneous recovery underwent greater response loss across additional extinction than one lacking recovery. They also showed that an excitor extinguished in compound with a CS showing recovery suffered greater response loss than an excitor extinguished in compound with a CS lacking recovery. Further, extinction of a compound composed of two CSs, one showing recovery and a second lacking recovery, produced greater extinction to the CS that showed recovery. These results show that spontaneous recovery of extinguished responses deepens their extinction through an error-correction mechanism regulated by both common and individual error terms. The third series of experiments studied the spontaneous recovery of latently inhibited and extinguished fear responses in within-subject designs. Using a compound test procedure, a CS that had received extensive preexposure or extensive extinction was found to have undergone greater spontaneous recovery relative to a CS just moderately preexposed or moderately extinguished. A CS given a mixed history of preexposure and extinction also underwent greater recovery relative to a CS just preexposed or just extinguished. These results suggest that both latent inhibition and extinction share a transient depressive process, and that the resulting recovery of responding is proportional to the amount of this depression.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 113-136).